During the impregnation stage of a Kraft cooking, dynamic changes occur in wood properties due to the alkali action. Particularly, its ion transport capacity, the effective capillary cross sectional area (ECCSA), is changed due to chemical reactions and swelling. In this work, the ECCSA in the transverse wood direction has been determined for Pinus sylvestris on the basis of the analogy between capillarity and electrical conductivity. Results show that the behavior of ECCSA can be associated with (a) the degree of removal of native acetyl groups and (b) the galactoglucomannan (GGM) losses due to peeling/stopping reactions and alkaline hydrolysis. Kinetic expressions for both reactions were discussed and a correlation between the ECCSA and both acetyl and GGM contents was established.

A deep understanding of alkali impregnation including the profiles of alkali concentration and hemicellulose degradation is necessary to analyze the optimization of current and innovative processes. In this paper, the impregnation of Scots pine (Pinus sylvestris L.) wood is analyzed and modeled under consideration of deacetylation, reactions of acidic group, and galactoglucomannan (GGM) degradation. The immobile anionic groups activated by the ionization of lignin-derived OH groups are also considered for the assessment of the Donnan effect. Predicted profiles of sodium and hydroxide ions and acetyl group concentrations are compared to experimental results. The balance between impregnation and hemicellulose degradation levels is discussed based on the developed models. Expectedly, higher concentrations and temperatures speed up the impregnation process. Nevertheless, a higher OH -concentration has two benefits for the same impregnation front position -the alkali charge inside the chip is higher and the GGM degradation is lower.

The relative ion transport capacity of wood -the "effective capillary cross sectional area" (ECCSA) -is determined in this work, based on the analogy with the relation between the electrical conductivities of wood and liquid medium. Wood was treated under different conditions and then the corresponding ECCSA A (the index A is for alkali) is estimated from the value obtained in an inert solution at room temperature (ECCSA Inert ). The difference between radial and tangential ECCSA A values is constant irrespective of pH, time, temperature and the presence of sodium sulfi de in the treatment liquor. The results show that ECCSA A is dependent on the degree of removal of native acetyl groups from hardwood O-acetyl-glucuronoxylan. A kinetic expression for Eucalyptus wood deacetylation is validated and used to establish the relationship between the acetyl content and ECCSA A in both anatomical directions.